1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine which has a function of making a determination on a property of a fuel supplied thereto.
2. Description of the Related Art
In many cases, a generally employed gasoline engine has fuel injection valves provided in intake pipes respectively, and the fuel injection valves inject a fuel toward intake ports respectively.
Although much of the injected fuel is directly sucked into cylinders during a suction stroke, the rest of the fuel adheres to inner wall surfaces of the intake ports or surfaces of intake valves and then gradually evaporates to be sucked into the cylinders. The fuel that has not evaporated is gradually sucked into the cylinders during or after a subsequent suction stroke.
As described above, the injected fuel is not entirely sucked into the cylinders during a single suction stroke. In other words, part of the fuel is sucked into the cylinders with a delay.
The adhesion of the fuel to the intake ports and the like causes fluctuations in air-fuel ratio when the engine enters a transient operational state. Especially when the engine is in a cold state, the fuel is unlikely to evaporate due to a low temperature in the vicinity of the intake ports, so the fluctuations in air-fuel ratio tend to become greater.
For instance, during cold start of the engine or during acceleration in a cold state, the fuel injection valves inject a large amount of the fuel, but the air-fuel ratio becomes lean owing to a temporary shortage of the fuel in the cylinders resulting from the fuel adherent to the intake ports and the like. This raises a problem in that unstable start-up of the engine leads to a deterioration in driveability and the contamination of exhaust gas.
With a view to solving this problem, in general, fuel injection control is performed in consideration of a fuel response delay ascribable to the fuel adherent to the intake ports and the like to suppress a deterioration in driveability and the contamination of exhaust gas.
However, the evaporation amount of the fuel changes depending on the property thereof, which is set differently according to a manufacturer, a season, or a sales territory.
For example, as a rule, a fuel referred to as summer gasoline is set lower in volatility than a fuel referred to as winter gasoline to prevent excessive volatilization from occurring due to high air temperatures in summer. For this reason, summer gasoline is referred to as low volatile fuel, whereas winter gasoline is referred to as high volatile fuel.
When a driver adds low volatile fuel to his vehicle in a case where fuel injection controls are calibrated for standard fuel (for example fuel for emission regulations), a lean air-fuel ratio is generated due to the fact that low volatile fuel has lower volatility than standard fuel. Therefore, problems such as a deterioration in driveability and the contamination of exhaust gas are caused. Such problems arise when the engine enters a transient operational state as a result of, for example, start-up or acceleration/deceleration so that a great change is caused in fuel injection amount.
Thus, in order to solve the above-mentioned problems, a conventional control apparatus for an internal combustion engine is equipped with intake air amount control means, ignition timing control means, catalyst heat-up promoting means, and lean control means.
The intake air amount control means controls an intake air amount of the internal combustion engine. The ignition timing control means controls an ignition timing of the internal combustion engine. The catalyst heat-up promoting means increases the intake air amount immediately after the start of the internal combustion engine, and performs control for retarding the ignition timing such that the rotational speed of the internal combustion engine coincides with a target rotational speed. The lean control means performs control such that the air-fuel ratio of a mixture supplied to the internal combustion engine immediately after the start thereof becomes lean with respect to a stoichiometric air-fuel ratio, and suppresses a degree of leanness of the air-fuel ratio when the retardation amount of the ignition timing during operation of the catalyst heat-up promoting means does not reach a predetermined retardation amount (e.g., see JP 2001-182591 A).
A conventional fuel property determining apparatus for an internal combustion engine is equipped with a fuel injection valve, an air-fuel ratio sensor, wet amount control means, and fuel property determining means.
The fuel injection valve injects fuel. The air-fuel ratio sensor detects an air-fuel ratio of exhaust gas or whether the air-fuel ratio is rich or lean. The wet amount control means performs control for reducing a wet amount, namely, an amount of fuel adherent to an intake system, which has been injected from the fuel injection valve prior to the activation of the air-fuel ratio sensor, and ends this control to increase the wet amount after the activation of the air-fuel ratio sensor. The fuel property determining means makes a determination on fuel property based on an output of the air-fuel ratio sensor or a control parameter that changes in accordance therewith, after the activation of the air-fuel ratio sensor (e.g., see JP 2002-309995 A).
In the conventional control apparatus for the internal combustion engine disclosed in JP 2001-182591 A, the influence of a fuel response delay emerges only when the engine enters a transient operational state. Therefore, no change is caused in fuel injection amount when the rotational speed of the engine is held constant.
Thus, there is caused a problem in that the accuracy in making a determination on fuel property decreases to the extent of bringing about an erroneous determination.
In the fuel property determining apparatus for the internal combustion engine disclosed in JP 2002-309995 A, the timing for opening an intake valve needs to be set at or past a top dead center so as to perform the control for reducing the wet amount.
Thus, it becomes necessary to set special variable timings for opening/closing the intake valve. As a result, there is also caused a problem of a cost increase.